2025 Volume 25 Issue 3 Pages 127-135
The falling-film-type heat exchanger used in this study is expected to achieve high efficiency in heat exchange by utilizing the falling film. With this heat exchanger, the heating medium flows inside the heat exchanger tube and the falling liquid film flows on the outer surface of the heat exchanger tube to exchange heat. Our previous studies revealed the basic heat transfer characteristics of the falling-film-type heat exchanger; developed design equations applicable to a limited scope; demonstrated the possibility of improving performance by inserting a variety of shafts with screw blades into the heat exchanger tube; and clarified that the heat exchange performance can be improved by improving the liquid film flow condition on the outer surface of the heat exchanger tube. In this study, we investigate the relationship between the liquid film thickness and heat transfer characteristics for the falling-film-type heat exchangers of horizontal-tube-type, and consider the modification of dimensionless numbers that can uniformly evaluate the heat transfer coefficients on the liquid film side of this type and another type (vertical-plate-type in this study) of falling film heat exchangers. Furthermore, we attempt to derive a dimensionless equation for the liquid film side heat transfer coefficient using the Wilson plot method. As a result, the heat transfer characteristics of the falling-film-type heat exchangers of horizontal-tube-type were clarified to some extent, and a dimensionless equation for the heat transfer coefficient on the liquid film side using the modified Nusselt number was proposed.
